In order to bind heavy articles, such as, for example, strip coils, tubes, stacked plates, and the like, it is normally required that such articles be wound or bound with or by means of a binding strap exhibiting a high degree of tension, such as, for example, a steel band, the degree of tension being in fact of such a degree as to have a value which is close to the tensile strength of the steel band at which the steel band will tend to break. Upon achieving the predetermined degree of tension, the strap end portions are then bonded to each other so as to complete the binding operation.
With reference initially being made to FIG. 5, there is schematically shown one example of a conventional binding machine of the aforenoted type within which the strap-binding operation may be carried out by means of a multi-functional binding head 1 which is vertically movable with respect to the binding machine frame, and in connection with which the apparatus of the present invention may be employed.
More particularly, a band-like binding strap 3 is interposed between a pair of operating wheels 2 of the binding head 1 so as to be held therebetween and fed in a direction shown by means of an arrow f as a result of the rotation of both wheels 2 in a first forward direction. The strap is wound around articles 4 to be bound, through means of one revolution thereabout, and the leading or forward end portion 3a of the strap 3 is gripped by means of a gripping unit, not shown, disposed within the binding head 1. The trailing or rear end portion 3b of the binding strap 3 is taken up or retracted in the opposite direction shown by means of the arrow tt as a result of the rotation of the wheels 2 in a second reverse direction, thereby causing the strap 3 to bind the article 4 without any looseness or slack. In particular, the trailing end portion 3b of the strap 3 is grasped and moved in the reverse direction tt so as to strongly tension the entire strap 3 disposed around the article 4, whereupon the overlapping portions of the binding strap 3, comprising the leading or forward end portion 3a and the trailing or rear end portion 3b, are bonded together, while under such tensioned conditions, by means of a suitable bonding or fusing mechanism, not shown, disposed within the binding head 1.
After the overlapping strap portions 3a and 3b have been bonded to each other, the strap portion 3c disposed upstream of the bonded junction defined between straps portions 3a and 3b is cut and separated from the article-encircling binding strap 3. It is additionally noted that when the head portion which has served as an underlying foundation for the bonded strap portions is transversely removed, the bonded strap portion is loosened to a predetermined extent corresponding to the thickness of the removed head portion, or in other words, by the amount defined by means of the gap residually defined by means of the removed head portion. However, such looseness is in fact absorbed within a predetermined range characterized by the inherent resiliency within the binding strap, and the tension developed therein, such that the residual tension still present within the binding strap is sufficient to retain a strong binding state with respect to the article 4 being bound.
Continuing further, in accordance with the conventional apparatus as shown in FIG. 6, one of the operating wheels 2 comprises a traction wheel 2T which is provided with a grooved peripheral surface, while the other operating wheel comprises a back-up wheel 2B having a smooth peripheral surface. The backup wheel 2B is rotatably supported so as to rotate about an axis b with respect to the frame of the binding head 1, while the traction wheel 2T is rotatably supported so as to be rotatable about an axis t which is displaced with respect to a pivotal axis X of an eccentric housing 5 by means of an eccentric amount x. The system is so constructed that when the eccentric housing 5 is pivoted about its axis X by means of a spring 6 interposed between the eccentric housing 5 and the frame of the binding head 1, the traction wheel 2T undergoes eccentric movement so as to come into contact with the back-up wheel 2B.
Consequently, it is to be appreciated that the strap 3 can be fed in the first forward direction f, and taken up or retracted in the second reverse direction tt as a result of a relatively small biasing force developed by means of the spring 6, and as a result of a relatively small amount of torque as developed by means of the drive system. Continuing further, when a large amount of resistance is encountered, such as, for example, during the final stage of taking up or retracting the strap 3, that is, during the tightening or tensioning of the strap 3 in order to achieve the encircled binding of the article 4, the drive system is switched so as to be operable within a low-speed, high-torque mode. Such an operation applies a large degree of tension to the binding strap, and such tension causes both wheels to be disposed in contact with each other with a small wedge angle .alpha. defined therebetween and wherein the wheels tend to move in the direction f so as to, in turn, tend to reduce the wedge angle .alpha., as is seen in FIG. 6. Accordingly, the contact force developed between the wheels is increased by means of such wedging effect whereby a high degree of tensioning of the binding strap in the direction tt is effectively achieved in a self-energizing manner in view of the fact that the strap tension will increase as a function of the increasing contact force developed or generated between the operating wheels 2T and 2B.
The steel-band strap 3 employed within the aforenoted type of apparatus conventionally has a width of 0.75-1.25 inches (19-32 mm), a thickness of approximately 0.9 mm, and a tensile strength of approximately 75-100 kgs/mm.sup.2. Consequently, the strap is especially well-suited for high-tension forces applied thereto during the strap-tensioning operation, and in fact can withstand pressure contact forces which are several magnitudes greater than that of its tensile strength. It is lastly noted that the gap defined between the operating wheels 2T and 2B is designated as g.
According to the conventional apparatus, when both wheels are brought to their respective positions wherein the strap is held therebetween and the aforenoted self-energizing tensioning process effectively proceeds accordingly, the final-stage wedge angle .alpha. is within the range of approximately 5.degree.-6.degree., and the gap g defined between the wheels 2T and 2B is smaller as compared with respect to the strap thickness. It is of course appreciated that the gap g will undergo small variations with respect to, or as a function of, the variations of the angle .alpha. when the latter has a value which is within the vicinity of the aforenoted small-angle range. Accordingly, during the time that sledding takes place wherein the leading end or tip of the strap is introduced between both wheels 2T and 2B by increasing the size of the gap g, it is required that the gap g be increased to a size approximately equal to 2.5 mm which includes a surplus amount of space or width of the gap so as to compensate for, or accommodate, any variations in the strap thickness or irregularities attendant the configuration or shape of the cut leading end or tip portion of the strap. In this connection, the moving and operating angle of a handle 7, which is attached to the eccentric housing 5, should be substantial. This requirement, however, increases the displacement movement of the eccentric housing 5 and its relevant drive system. Such, in turn, requires the overall apparatus to be significantly large in size. Furthermore, since the lever operation must also be carried out against the load of the spring 6, the resistance encountered is significantly increased.